Vapor deposition apparatus and process for continuous deposition of a thin film layer on a substrate

ABSTRACT

An apparatus and related process are provided for vapor deposition of a sublimated source material as a thin film on a photovoltaic (PV) module substrate. A receptacle is disposed within a vacuum head chamber and is configured for receipt of a source material. A heated distribution manifold is disposed below the receptacle and includes a plurality of passages defined therethrough. The receptacle is indirectly heated by the distribution manifold to a degree sufficient to sublimate source material within the receptacle. A molybdenum distribution plate is disposed below the distribution manifold and at a defined distance above a horizontal plane of a substrate conveyed through the apparatus. The molybdenum distribution plate includes a pattern of holes therethrough that further distribute the sublimated source material passing through the distribution manifold onto the upper surface of the underlying substrate. The molybdenum distribution plate includes greater than about 75% by weight molybdenum.

PRIORITY INFORMATION

The present application claims priority to, and is a divisionalapplication of, U.S. patent application Ser. No. 12/639,043 titled“Vapor Deposition Apparatus and Process for Continuous Deposition of aThin Film Layer on a Substrate” filed on Dec. 16, 2009 by Rathweg, etal., which is incorporated by reference herein.

FIELD OF THE INVENTION

The subject matter disclosed herein relates generally to the field ofthin film deposition processes wherein a thin film layer, such as asemiconductor material layer, is deposited on a substrate. Moreparticularly, the subject matter is related to a vapor depositionapparatus and associated process for depositing a thin film layer of aphoto-reactive material on a glass substrate in the formation ofphotovoltaic (PV) modules.

BACKGROUND OF THE INVENTION

Thin film photovoltaic (PV) modules (also referred to as “solar panels”)based on cadmium telluride (CdTe) paired with cadmium sulfide (CdS) asthe photo-reactive components are gaining wide acceptance and interestin the industry. CdTe is a semiconductor material having characteristicsparticularly suited for conversion of solar energy to electricity. Forexample, CdTe has an energy bandgap of about 1.45 eV, which enables itto convert more energy from the solar spectrum as compared to lowerbandgap semiconductor materials historically used in solar cellapplications (e.g., about 1.1 eV for silicon). Also, CdTe convertsradiation energy in lower or diffuse light conditions as compared to thelower bandgap materials and, thus, has a longer effective conversiontime over the course of a day or in cloudy conditions as compared toother conventional materials.

Solar energy systems using CdTe PV modules are generally recognized asthe most cost efficient of the commercially available systems in termsof cost per watt of power generated. However, the advantages of CdTe notwithstanding, sustainable commercial exploitation and acceptance ofsolar power as a supplemental or primary source of industrial orresidential power depends on the ability to produce efficient PV moduleson a large scale and in a cost effective manner.

Certain factors greatly affect the efficiency of CdTe PV modules interms of cost and power generation capacity. For example, CdTe isrelatively expensive and, thus, efficient utilization (i.e., minimalwaste) of the material is a primary cost factor. In addition, the energyconversion efficiency of the module is a factor of certaincharacteristics of the deposited CdTe film layer. Non-uniformity ordefects in the film layer can significantly decrease the output of themodule, thereby adding to the cost per unit of power. Also, the abilityto process relatively large substrates on an economically sensiblecommercial scale is a crucial consideration.

CSS (Closed System Sublimation) is a known commercial vapor depositionprocess for production of CdTe modules. Reference is made, for example,to U.S. Pat. No. 6,444,043 and U.S. Pat. No. 6,423,565. Within the vapordeposition chamber in a CSS system, the substrate is brought to anopposed position at a relatively small distance (i.e., about 2-3 mm)opposite to a CdTe source. The CdTe material sublimes and deposits ontothe surface of the substrate. In the CSS system of U.S. Pat. No.6,444,043 cited above, the CdTe material is in granular form and is heldin a heated receptacle within the vapor deposition chamber. Thesublimated material moves through holes in a cover placed over thereceptacle and deposits onto the stationary glass surface, which is heldat the smallest possible distance (1-2 mm) above the cover frame.

Since the best film quality of a thin film is achieved in a narrowtemperature range just below the point at which the film would beginsublimating off faster than it is depositing (e.g., between about 600°C. to about 650° C. for cadmium telluride), it is desired to keep thesubstrate temperature between this narrow temperature range throughoutthe CSS process. However, in a CSS process, the cover must be heated toa temperature considerably greater (e.g., about 800° C. when depositingcadmium telluride) than the substrate to ensure that no materialdeposits and builds up on the cover. Since the cover is hotter than thesubstrate, the cover will raise the temperature of the substrate throughradiation (e.g., heat exchange) from the cover. This temperature gaincan result in a gradient of film quality through the thickness of thefilm, due to a temperature increase of the substrate during thedeposition of the thin film. Further, if the temperature gain of thesubstrate is too high, the film thickness is limited because thesubstrate may have become too hot to receive any additional material.This would require that the process begin with the substrate at a lowertemperature, resulting in the first film deposited being lower incrystalline quality.

Accordingly, there exists an ongoing need in the industry for animproved vapor deposition apparatus and process for economicallyfeasible large scale production of efficient PV modules, particularlyCdTe modules. In particular, a need exists for an improved sublimationplate for use in an economically feasible large scale production ofefficient PV modules, particularly CdTe modules, in a CSS process.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

An apparatus is generally provided for vapor deposition of a sublimatedsource material as a thin film on a photovoltaic (PV) module substrate.In one embodiment, the apparatus can include a deposition head. Areceptacle can be disposed in the deposition head and configured forreceipt of a granular source material. A heated distribution manifoldcan be disposed below the receptacle allowing the receptacle to beindirectly heated by the distribution manifold to a degree sufficient tosublimate source material within the receptacle. The heated distributionmanifold can define a plurality of passages therethrough. A molybdenumdeposition plate can be disposed below the distribution manifold and ata defined distance above a horizontal conveyance plane of an uppersurface of a substrate conveyed through the apparatus. The molybdenumdistribution plate can also define a pattern of passages therethroughthat further distribute the sublimated source material passing throughthe distribution manifold. The molybdenum distribution plate includesgreater than about 75% by weight molybdenum.

A process is also provided for vapor deposition of a sublimated sourcematerial to form thin film on a photovoltaic (PV) module substrate. Forexample, a source material can be supplied to a receptacle within adeposition head. The receptacle can be indirectly heated with a heatsource member disposed below the receptacle to sublimate the sourcematerial. The sublimated source material can be directed downwardlywithin the deposition head through the heat source member whileindividual substrates are conveyed below the heat source member. Thesublimated source material that passes through the heat source membercan be distributed onto an upper surface of the substrates via amolybdenum distribution plate posited between the upper surface of thesubstrate and the heat source member such that leading and trailingsections of the substrates in the direction of conveyance are exposed togenerally the same vapor deposition conditions to achieve a desiredsubstantially uniform thickness of the thin film layer on the uppersurface of the substrates, wherein said molybdenum distribution platecomprises greater than about 75% by weight molybdenum.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWING

A full and enabling disclosure of the present invention, including thebest mode thereof, is set forth in the specification, which makesreference to the appended drawings, in which:

FIG. 1 is a plan view of a system that may incorporate embodiments of avapor deposition apparatus of the present invention;

FIG. 2 is a cross-sectional view of an embodiment of a vapor depositionapparatus according to aspects of the invention in a first operationalconfiguration;

FIG. 3 is a cross-sectional view of the embodiment of FIG. 2 in a secondoperational configuration;

FIG. 4 is a cross-sectional view of the embodiment of FIG. 2 incooperation with a substrate conveyor; and,

FIG. 5 is a top view of the receptacle component within the embodimentof FIG. 2.

Repeat use of reference characters in the present specification anddrawings is intended to represent the same or analogous features orelements.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

In the present disclosure, when a layer is being described as “on” or“over” another layer or substrate, it is to be understood that thelayers can either be directly contacting each other or have anotherlayer or feature between the layers. Thus, these terms are simplydescribing the relative position of the layers to each other and do notnecessarily mean “on top of” since the relative position above or belowdepends upon the orientation of the device to the viewer. Additionally,although the invention is not limited to any particular film thickness,the term “thin” describing any film layers of the photovoltaic devicegenerally refers to the film layer having a thickness less than about 10micrometers (“microns” or “μm”).

It is to be understood that the ranges and limits mentioned hereininclude all ranges located within the prescribed limits (i.e.,subranges). For instance, a range from about 100 to about 200 alsoincludes ranges from 110 to 150, 170 to 190, 153 to 162, and 145.3 to149.6. Further, a limit of up to about 7 also includes a limit of up toabout 5, up to 3, and up to about 4.5, as well as ranges within thelimit, such as from about 1 to about 5, and from about 3.2 to about 6.5.

FIG. 1 illustrates an embodiment of a system 10 that may incorporate avapor deposition apparatus 100 (FIGS. 2 through 5) in accordance withembodiments of the invention configured for deposition of a thin filmlayer on a photovoltaic (PV) module substrate 14 (referred to hereafteras a “substrate”). The thin film may be, for example, a film layer ofcadmium telluride (CdTe). As mentioned, it is generally recognized inthe art that a “thin” film layer on a PV module substrate is generallyless than about 10 microns (μm).

The vapor deposition apparatus 100 includes a distribution plate 152disposed below the distribution manifold 124 at a defined distance abovea horizontal plane of the upper surface of an underlying substrate 14,as depicted in FIG. 4. The distribution plate 152 defines a pattern ofpassages, such as holes, slits, and the like, therethrough that furtherdistribute the sublimated source material passing through thedistribution manifold 124 such that the source material vapors areuninterrupted in the transverse direction. In other words, the patternof passages are shaped and staggered or otherwise positioned to ensurethat the sublimated source material is deposited completely over thesubstrate in the transverse direction so that longitudinal streaks orstripes of “un-coated” regions on the substrate are avoided.

During use, the deposition plate 152 is heated to a temperature abovethe temperature of the substrate 14 to ensure that no material depositsand builds up on the deposition plate 152. For example, when depositinga thin film cadmium telluride layer, the substrate 14 may be heated to asubstrate temperature between about 550° C. and about 700° C. (e.g.,between about 600° C. and about 650° C.) while the deposition plate maybe heated to a plate temperature above about 725° C., such as from about750° C. to about 900° C. (e.g., from about 800° C. to about 850° C.).However, heat transfer between the deposition plate 152 and thesubstrate 14 may be minimized by controlling the chemical make-up of thedeposition plate 152.

According to the present invention, the deposition plate 152 is amolybdenum deposition plate 152. Generally, molybdenum has thesufficient thermal properties to ensure substantially uniform heatingthroughout the molybdenum deposition plate 152 while minimizing thermalexchange between the molybdenum deposition plate 152 and the substrate14 during deposition. For example, molybdenum has an extremely highmelting point (i.e., about 2623° C.) allowing a molybdenum shield to beheated to extreme temperatures without fear of melting or otherwisedamaging the shield. Additionally, molybdenum has a low coefficient ofthermal expansion (i.e., about 4.8μ·m⁻¹·K⁻¹ at 25° C.), while havingsufficient thermal conductivity (i.e., about 138 W·m⁻¹·K⁻¹ at 26.8° C.),which allows it to remain substantially the same shape upon heatingwhile still providing minimal thermal transfer via radiation to thenearby substrate 14. Molybdenum has an emissivity coefficient of about0.06 at 38° C., of about 0.08 at 260° C., of about 0.11 at 538° C., andof about 0.18 at 1093° C. As is known in the art, an emissivitycoefficient of a surface is calculated according the Stefan-BoltzmannLaw comparing the surface with the radiation of heat from a ideal “blackbody” with the emissivity coefficient e=1 at a given temperature. Thisemissivity of molybdenum is considerably lower than graphitized carbon,which has an emissivity coefficient of about 0.76 at 100° C., of about0.75 at 300° C., and about 0.71 at 500° C. Finally, molybdenum has arelatively high resistance to corrosion and wear. Thus, a molybdenumdeposition plate 152 can be in use in the deposition head many times,including heating and cooling, to sputter layers in a commercial-scalemanufacturing setting.

As used herein, the term “molybdenum deposition plate” refers todeposition plates including greater than about 75% by weight molybdenum,such as greater than about 85% by weight molybdenum. In someembodiments, the molybdenum deposition plate 152 can include greaterthan about 95% by weight molybdenum, such as from about 97.5% to 100% byweight molybdenum (e.g., greater than about 99.5%). In particularembodiments, the molybdenum deposition plate 152 can consist essentiallyof molybdenum (i.e., the shield is substantially free from othermetals), and, in one particular embodiment, the molybdenum depositionplate 152 can consist of molybdenum (i.e., substantially 100% puremolybdenum).

Accordingly, the actual temperature increase of the substrate 14 in thedeposition vapor deposition apparatus 100 having a molybdenum depositionplate 152 can depend on a number of factors. For example, the speed oftravel of the substrate 14 through the apparatus 100 affects the lengthof time the substrate 14 is exposed to the increased temperatures in thevapor deposition apparatus 100 and can affect the temperature gain.However, in particular embodiments where a cadmium telluride layer isformed to a thickness between about 1 and 5 μm, the substrate 14 canincrease in temperature no more than about 75° C. during depositionwithin the vapor deposition apparatus 100, such as from about 10° C. toabout 60° C. Put another way, the substrate temperature of the substrate14 can increase by no more than about 15% of its initial temperatureentering the vapor deposition apparatus 100 prior to exiting the vapordeposition apparatus 100, such as from about 2% to about 10%.

It should be appreciated that the present vapor deposition apparatus 100is not limited to use in the system 10 illustrated in FIG. 1, but may beincorporated into any suitable processing line configured for vapordeposition of a thin film layer onto a PV module substrate 14. Forreference and an understanding of an environment in which the vapordeposition apparatus 100 may be used, the system 10 of FIG. 1 isdescribed below, followed by a detailed description of the apparatus100.

Referring to FIG. 1, the exemplary system 10 includes a vacuum chamber12 defined by a plurality of interconnected modules, including aplurality of heater modules 16 that define a pre-heat section of thevacuum chamber 12 through which the substrates 14 are conveyed andheated to a desired temperature before being conveyed into the vapordeposition apparatus 100. Each of the modules 16 may include a pluralityof independently controlled heaters 18, with the heaters defining aplurality of different heat zones. A particular heat zone may includemore than one heater 18.

The vacuum chamber 12 also includes a plurality of interconnectedcool-down modules 20 downstream of the vapor deposition apparatus 100.The cool-down modules 20 define a cool-down section within the vacuumchamber 12 through which the substrates 14 having the thin film ofsublimated source material deposited thereon are conveyed and cooled ata controlled cool-down rate prior to the substrates 14 being removedfrom the system 10. Each of the modules 20 may include a forced coolingsystem wherein a cooling medium, such as chilled water, refrigerant, orother medium, is pumped through cooling coils (not illustrated)configured with the modules 20.

In the illustrated embodiment of system 10, at least one post-heatmodule 22 is located immediately downstream of the vapor depositionapparatus 100 and upstream of the cool-down modules 20 in a conveyancedirection of the substrates. As the leading section of a substrate 14 isconveyed out of the vapor deposition apparatus 100, it moves into thepost-heat module 22, which maintains the temperature of the substrate 14at essentially the same temperature as the trailing portion of thesubstrate still within the vapor deposition apparatus 100. In this way,the leading section of the substrate 14 is not allowed to cool while thetrailing section is still within the vapor deposition apparatus 100. Ifthe leading section of a substrate 14 were allowed to cool as it exitedthe apparatus 100, a non-uniform temperature profile would be generatedlongitudinally along the substrate 14. This condition could result inthe substrate breaking from thermal stress.

As diagrammatically illustrated in FIG. 1, a feed device 24 isconfigured with the vapor deposition apparatus 100 to supply sourcematerial, such as granular CdTe. The feed device 24 may take on variousconfigurations within the scope and spirit of the invention, andfunctions to supply the source material without interrupting thecontinuous vapor deposition process within the apparatus 100 orconveyance of the substrates 14 through the apparatus 100.

Still referring to FIG. 1, the individual substrates 14 are initiallyplaced onto a load conveyor 26, and are subsequently moved into an entryvacuum lock station that includes a load module 28 and a buffer module30. A “rough” (i.e., initial) vacuum pump 32 is configured with the loadmodule 28 to draw an initial vacuum, and a “fine” (i.e., final) vacuumpump 38 is configured with the buffer module 30 to increase the vacuumin the buffer module 30 to essentially the vacuum pressure within thevacuum chamber 12. Slide gates or valves 34 are operably disposedbetween the load conveyor 26 and the load module 28, between the loadmodule 28 and the buffer module 30, and between the buffer module 30 andthe vacuum chamber 12. These valves 34 are sequentially actuated by amotor or other type of actuating mechanism 36 in order to introduce thesubstrates 14 into the vacuum chamber 12 in a step-wise manner withoutaffecting the vacuum within the chamber 12.

In operation of the system 10, an operational vacuum is maintained inthe vacuum chamber 12 by way of any combination of rough and/or finevacuum pumps 40. In order to introduce a substrate 14 into the vacuumchamber 12, the load module 28 and buffer module 30 are initially vented(with the slide valve 34 between the two modules in the open position).The slide valve 34 between the buffer module 30 and the first heatermodule 16 is closed. The slide valve 34 between the load module 28 andload conveyor 26 is opened and a substrate 14 is moved into the loadmodule 28. At this point, the first slide valve 34 is shut and the roughvacuum pump 32 then draws an initial vacuum in the load module 28 andbuffer module 30. The substrate 14 is then conveyed into the buffermodule 30, and the slide valve 34 between the load module 28 and buffermodule 30 is closed. The fine vacuum pump 38 then increases the vacuumin the buffer module 30 to approximately the same vacuum in the vacuumchamber 12. At this point, the slide valve 34 between the buffer module30 and vacuum chamber 12 is opened and the substrate 14 is conveyed intothe first heater module 16.

An exit vacuum lock station is configured downstream of the lastcool-down module 20, and operates essentially in reverse of the entryvacuum lock station described above. For example, the exit vacuum lockstation may include an exit buffer module 42 and a downstream exit lockmodule 44. Sequentially operated slide valves 34 are disposed betweenthe buffer module 42 and the last one of the cool-down modules 20,between the buffer module 42 and the exit lock module 44, and betweenthe exit lock module 44 and an exit conveyor 46. A fine vacuum pump 38is configured with the exit buffer module 42, and a rough vacuum pump 32is configured with the exit lock module 44. The pumps 32, 38 and slidevalves 34 are sequentially operated to move the substrates 14 out of thevacuum chamber 12 in a step-wise fashion without loss of vacuumcondition within the vacuum chamber 12.

System 10 also includes a conveyor system configured to move thesubstrates 14 into, through, and out of the vacuum chamber 12. In theillustrated embodiment, this conveyor system includes a plurality ofindividually controlled conveyors 48, with each of the various modulesincluding a respective one of the conveyors 48. It should be appreciatedthat the type or configuration of the conveyors 48 may vary. In theillustrated embodiment, the conveyors 48 are roller conveyors havingrotatably driven rollers that are controlled so as to achieve a desiredconveyance rate of the substrates 14 through the respective module andthe system 10 overall.

As described, each of the various modules and respective conveyors inthe system 10 are independently controlled to perform a particularfunction. For such control, each of the individual modules may have anassociated independent controller 50 configured therewith to control theindividual functions of the respective module. The plurality ofcontrollers 50 may, in turn, be in communication with a central systemcontroller 52, as diagrammatically illustrated in FIG. 1. The centralsystem controller 52 can monitor and control (via the independentcontrollers 50) the functions of any one of the modules so as to achievean overall desired heat-up rate, deposition rate, cool-down rate,conveyance rate, and so forth, in processing of the substrates 14through the system 10.

Referring to FIG. 1, for independent control of the individualrespective conveyors 48, each of the modules may include any manner ofactive or passive sensors 54 that detects the presence of the substrates14 as they are conveyed through the module. The sensors 54 are incommunication with the respective module controller 50, which is in turnin communication with the central controller 52. In this manner, theindividual respective conveyor 48 may be controlled to ensure that aproper spacing between the substrates 14 is maintained and that thesubstrates 14 are conveyed at the desired conveyance rate through thevacuum chamber 12.

FIGS. 2 through 5 relate to a particular embodiment of the vapordeposition apparatus 100. Referring to FIGS. 2 and 3 in particular, theapparatus 100 includes a deposition head 110 defining an interior spacein which a receptacle 116 is configured for receipt of a granular sourcematerial (not shown). As mentioned, the granular source material may besupplied by a feed device or system 24 (FIG. 1) via a feed tube 148(FIG. 4). The feed tube 148 is connected to a distributor 144 disposedin an opening in a top wall 114 of the deposition head 110. Thedistributor 144 includes a plurality of discharge ports 146 that areconfigured to evenly distribute the granular source material into thereceptacle 116. The receptacle 116 has an open top and may include anyconfiguration of internal ribs 120 or other structural elements.

In the illustrated embodiment, at least one thermocouple 122 isoperationally disposed through the top wall 114 of the deposition head110 to monitor temperature within the deposition head 110 adjacent to orin the receptacle 116.

The deposition head 110 also includes longitudinal end walls 112 andside walls 113 (FIG. 5). Referring to FIG. 5 in particular, thereceptacle 116 has a shape and configuration such that the end walls 118are spaced from the end walls 112 of the head chamber 110. The sidewalls 117 of the receptacle 116 lie adjacent to and in close proximationto the side walls 113 of the deposition head so that very littleclearance exists between the respective walls, as depicted in FIG. 5.With this configuration, sublimated source material will flow out of theopen top of the receptacle 116 and downwardly over the end walls 118 asleading and trailing curtains of vapor 119 over, as depicted in FIGS. 2,3, and 5. Very little of the sublimated source material will flow overthe side walls 117 of the receptacle 116.

A heated distribution manifold 124 is disposed below the receptacle 116.This distribution manifold 124 may take on various configurations withinthe scope and spirit of the invention, and serves to indirectly heat thereceptacle 116, as well as to distribute the sublimated source materialthat flows from the receptacle 116. In the illustrated embodiment, theheated distribution manifold 124 has a clam-shell configuration thatincludes an upper shell member 130 and a lower shell member 132. Each ofthe shell members 130, 132 includes recesses therein that definecavities 134 when the shell members are mated together as depicted inFIGS. 2 and 3. Heater elements 128 are disposed within the cavities 134and serve to heat the distribution manifold 124 to a degree sufficientfor indirectly heating the source material within the receptacle 116 tocause sublimation of the source material. The heater elements 128 may bemade of a material that reacts with the source material vapor and, inthis regard, the shell members 130, 132 also serve to isolate the heaterelements 128 from contact with the source material vapor. The heatgenerated by the distribution manifold 124 is also sufficient to preventthe sublimated source material from plating out onto components of thehead chamber 110. Desirably, the coolest component in the head chamber110 is the upper surface of the substrates 14 conveyed therethrough soas to ensure that the sublimated source material plates onto thesubstrate, and not onto components of the head chamber 110.

Still referring to FIGS. 2 and 3, the heated distribution manifold 124includes a plurality of passages 126 defined therethrough. Thesepassages have a shape and configuration so as to uniformly distributethe sublimated source material towards the underlying substrates 14(FIG. 4).

In the illustrated embodiment, the distribution plate 152 is disposedbelow the distribution manifold 124 at a defined distance above ahorizontal plane of the upper surface of an underlying substrate 14, asdepicted in FIG. 4. This distance may be, for example, between about 0.3cm to about 4.0 cm. In a particular embodiment, the distance is about1.0 cm. The conveyance rate of the substrates below the distributionplate 152 may be in the range of, for example, about 10 mm/sec to about40 mm/sec. In a particular embodiment, this rate may be, for example,about 20 mm/sec. The thickness of the CdTe film layer that plates ontothe upper surface of the substrate 14 can vary within the scope andspirit of the invention, and may be, for example, between about 1 micronto about 5 microns. In a particular embodiment, the film thickness maybe about 3 microns. The distribution plate 152 is a molybdenumdistribution plate 152 as described in greater detail above.

As previously mentioned, a significant portion of the sublimated sourcematerial will flow out of the receptacle 116 as leading and trailingcurtains of vapor 119, as depicted in FIG. 5. Although these curtains ofvapor 119 will diffuse to some extent in the longitudinal directionprior to passing through the distribution plate 152, it should beappreciated that it is unlikely that a uniform distribution of thesublimated source material in the longitudinal direction will beachieved. In other words, more of the sublimated source material will bedistributed through the longitudinal end sections of the distributionplate 152 as compared to the middle portion of the distribution plate.However, as discussed above, because the system 10 conveys thesubstrates 14 through the vapor deposition apparatus 100 at a constant(non-stop) linear speed, the upper surfaces of the substrates 14 will beexposed to the same deposition environment regardless of anynon-uniformity of the vapor distribution along the longitudinal aspectof the apparatus 100. The passages 126 in the distribution manifold 124and the holes in the distribution plate 152 ensure a relatively uniformdistribution of the sublimated source material in the transverse aspectof the vapor deposition apparatus 100. So long as the uniform transverseaspect of the vapor is maintained, a relatively uniform thin film layeris deposited onto the upper surface of the substrates 14 regardless ofany non-uniformity in the vapor deposition along the longitudinal aspectof the apparatus 100.

As illustrated in the figures, it may be desired to include a debrisshield 150 between the receptacle 116 and the distribution manifold 124.This shield 150 includes holes defined therethrough (which may be largeror smaller than the size of the holes of the distribution plate 152) andprimarily serves to retain any granular or particulate source materialfrom passing through and potentially interfering with operation of themovable components of the distribution manifold 124, as discussed ingreater detail below. In other words, the debris shield 150 can beconfigured to act as a breathable screen that inhibits the passage ofparticles without substantially interfering with vapors 119 flowingthrough the shield 150.

Referring to FIGS. 2 through 4 in particular, apparatus 100 desirablyincludes transversely extending seals 154 at each longitudinal end ofthe head chamber 110. In the illustrated embodiment, the seals define anentry slot 156 and an exit slot 158 at the longitudinal ends of the headchamber 110. These seals 154 are disposed at a distance above the uppersurface of the substrates 14 that is less than the distance between thesurface of the substrates 14 and the distribution plate 152, as isdepicted in FIG. 4. The seals 154 help to maintain the sublimated sourcematerial in the deposition area above the substrates. In other words,the seals 154 prevent the sublimated source material from “leaking out”through the longitudinal ends of the apparatus 100. It should beappreciated that the seals 154 may be defined by any suitable structure.In the illustrated embodiment, the seals 154 are actually defined bycomponents of the lower shell member 132 of the heated distributionmanifold 124. It should also be appreciated that the seals 154 maycooperate with other structure of the vapor deposition apparatus 100 toprovide the sealing function. For example, the seals may engage againststructure of the underlying conveyor assembly in the deposition area.

Any manner of longitudinally extending seal structure 155 may also beconfigured with the apparatus 100 to provide a seal along thelongitudinal sides thereof. Referring to FIGS. 2 and 3, this sealstructure 155 may include a longitudinally extending side member that isdisposed generally as close as reasonably possible to the upper surfaceof the underlying convey surface so as to inhibit outward flow of thesublimated source material without frictionally engaging against theconveyor.

Referring to FIGS. 2 and 3, the illustrated embodiment includes amovable shutter plate 136 disposed above the distribution manifold 124.This shutter plate 136 includes a plurality of passages 138 definedtherethrough that align with the passages 126 in the distributionmanifold 124 in a first operational position of the shutter plate 136 asdepicted in FIG. 3. As can be readily appreciated from FIG. 3, in thisoperational position of the shutter plate 136, the sublimated sourcematerial is free to flow through the shutter plate 136 and through thepassages 126 in the distribution manifold 124 for subsequentdistribution through the plate 152. Referring to FIG. 2, the shutterplate 136 is movable to a second operational position relative to theupper surface of the distribution manifold 124 wherein the passages 138in the shutter plate 136 are misaligned with the passages 126 in thedistribution manifold 124. In this configuration, the sublimated sourcematerial is blocked from passing through the distribution manifold 124,and is essentially contained within the interior volume of the headchamber 110. Any suitable actuation mechanism, generally 140, may beconfigured for moving the shutter plate 136 between the first and secondoperational positions. In the illustrated embodiment, the actuationmechanism 140 includes a rod 142 and any manner of suitable linkage thatconnects the rod 142 to the shutter plate 136. The rod 142 is rotated byany manner of mechanism located externally of the head chamber 110.

The shutter plate 136 configuration illustrated in FIGS. 2 and 3 isparticularly beneficial in that, as desired, the sublimated sourcematerial can be quickly and easily contained within the head chamber 110and prevented from passing through to the deposition area above theconveying unit. This may be desired, for example, during start up of thesystem 10 while the concentration of vapors 119 within the head chamberbuilds to a sufficient degree to start the deposition process. Likewise,during shutdown of the system, it may be desired to maintain thesublimated source material within the head chamber 110 to prevent thematerial from condensing on the conveyor or other components of theapparatus 100.

Referring to FIG. 4, the vapor deposition apparatus 100 may furthercomprise a conveyor 160 disposed below the head chamber 110. Thisconveyor 160 may be uniquely configured for the deposition process ascompared to the conveyors 48 discussed above with respect to the system10 of FIG. 1. For example, the conveyor 160 may be a self-containedconveying unit that includes a continuous loop conveyor on which thesubstrates 14 are supported below the distribution plate 152. In theillustrated embodiment, the conveyor 160 is defined by a plurality ofslats 162 that provide a flat, unbroken (i.e., no gaps between theslats) support surface for the substrates 14. The slat conveyor isdriven in an endless loop around sprockets 164. It should beappreciated, however, that the invention is not limited to anyparticular type of conveyor 160 for moving the substrates 14 through thevapor deposition apparatus 100.

The present invention also encompasses various process embodiments forvapor deposition of a sublimated source material to form a thin film ona PV module substrate. The various processes may be practiced with thesystem embodiments described above or by any other configuration ofsuitable system components. It should thus be appreciated that theprocess embodiments according to the invention are not limited to thesystem configuration described herein.

In a particular embodiment, the vapor deposition process includessupplying source material to a receptacle within a deposition head, andindirectly heating the receptacle with a heat source member to sublimatethe source material. The sublimated source material is directed out ofthe receptacle and downwardly within the deposition head through theheat source member. Individual substrates are conveyed below the heatsource member. The sublimated source material that passes through theheat source is distributed onto an upper surface of the substrates suchthat leading and trailing sections of the substrates in the direction ofconveyance thereof are exposed to the same vapor deposition conditionsso as to achieve a desired uniform thickness of the thin film layer onthe upper surface of the substrates.

In a unique process embodiment, the sublimated source material isdirected from the receptacle primarily as transversely extending leadingand trailing curtains relative to the conveyance direction of thesubstrates. The curtains of sublimated source material are directeddownwardly through the heat source member towards the upper surface ofthe substrates. These leading and trailing curtains of sublimated sourcematerial may be longitudinally distributed to some extent relative tothe conveyance direction of the substrates after passing through theheat source member.

In yet another unique process embodiment, the passages for thesublimated source material through the heat source may be blocked withan externally actuated blocking mechanism, as discussed above.

Desirably, the process embodiments include continuously conveying thesubstrates at a substantially constant linear speed during the vapordeposition process.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

1. A process for vapor deposition of a sublimated source material toform thin film on a photovoltaic (PV) module substrate, the processcomprising: supplying source material to a receptacle within adeposition head; indirectly heating the receptacle with a heat sourcemember disposed below the receptacle to sublimate the source material;directing the sublimated source material downwardly within thedeposition head through the heat source member; conveying individualsubstrates below the heat source member; and, distributing thesublimated source material that passes through the heat source memberonto an upper surface of the substrates via a molybdenum distributionplate posited between the upper surface of the substrate and the heatsource member, wherein said molybdenum distribution plate comprisesgreater than about 75% by weight molybdenum.
 2. The process as in claim1, wherein leading and trailing sections of the substrates in thedirection of conveyance are exposed to generally the same vapordeposition conditions to achieve a desired substantially uniformthickness of the thin film layer on the upper surface of the substrates.3. The process as in claim 1, wherein said molybdenum distribution platecomprises greater than about 95% by weight molybdenum.
 4. The process asin claim 1, wherein said molybdenum distribution plate consistsessentially of molybdenum.
 5. The process as in claim 1, wherein saidmolybdenum distribution plate consists of molybdenum.
 6. The process asin claim 1, wherein the substrates are continuously conveyed at asubstantially constant linear conveyance rate during the vapordeposition process.
 7. The process as in claim 1, further comprising:heating the individual substrates to a substrate temperature prior toconveying individual substrates below the heat source member.
 8. Theprocess as in claim 7, wherein the substrate temperature is betweenabout 550° C. and about 700° C.
 9. The process as in claim 7, whereinthe substrate temperature is between about 600° C. and about 650° C. 10.The process as in claim 8, further comprising: heating the molybdenumdeposition plate to a plate temperature prior to distributing thesublimated source material that passes through the heat source memberonto the upper surface of the substrates via the molybdenum distributionplate.
 11. The process as in claim 10, wherein the plate temperature isabove about 725° C.
 12. The process as in claim 10, wherein the platetemperature is from about 750° C. to about 900° C.
 13. The process as inclaim 10, wherein the plate temperature is from about 800° C. to about850° C.
 14. The process as in claim 10, wherein the source materialcomprises cadmium telluride.
 15. The process as in claim 14, whereindistributing the sublimated source material that passes through the heatsource member onto the upper surface of the substrates via themolybdenum distribution plate forms a cadmium telluride layer on theupper surface that has a thickness between about 1 μm and 5 μm.
 16. Theprocess as in claim 1, further comprising: heating the individualsubstrates to a substrate temperature prior to conveying individualsubstrates below the heat source member; and heating the molybdenumdeposition plate to a plate temperature prior to distributing thesublimated source material that passes through the heat source memberonto the upper surface of the substrates via the molybdenum distributionplate.
 17. The process as in claim 16, wherein the substrate temperatureincreases no more than about 75° C. during deposition within the vapordeposition apparatus
 100. 18. The process as in claim 16, wherein thesubstrate temperature increases from about 10° C. to about 60° C. duringdeposition within the vapor deposition apparatus
 100. 19. The process asin claim 16, wherein the substrate temperature increases no more thanabout 15% of its initial temperature entering the vapor depositionapparatus 100 prior to exiting the vapor deposition apparatus
 100. 20.The process as in claim 16, wherein the substrate temperature increasesfrom about 2% to about 10% of its initial temperature entering the vapordeposition apparatus 100 prior to exiting the vapor deposition apparatus100.